Revert "drop eventing-rabbitmq downstream testing (#2969)"

[dprotaso]

This reverts commit bea8825.

Part of knative/eventing#7670

/assign @ikavgo
/assign @mkuratczyk
/assign @Zerpet

This ensures when people make changes to the shared library here we'll know if it breaks rabbitmq downstream

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.76%. Comparing base (03bf3de) to head (2b3256a).
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3008      +/-   ##
==========================================
+ Coverage   78.75%   78.76%   +0.01%     
==========================================
  Files         188      188              
  Lines       11107     8869    -2238     
==========================================
- Hits         8747     6986    -1761     
+ Misses       2094     1617     -477     
  Partials      266      266              

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[izabelacg]

/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, izabelacg

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[izabelacg]

/lgtm